1. Field of the Invention
The present invention relates to a brake device for a tape rule, and more particularly to an elaborately designed brake device for a type rule which can definitely control halting the tape in a desired position when it is pulled out for measurement.
2. Description of the Prior Art
A tape rule is widely applicable for surveying work both in domestic and engineering fields such as, interior design, furniture arrangement, civil engineering and building construction, etc. Incidentally it is found that a conventional tape rule has inherent shortcomings as follows:
1. Its brake device (a key button) is not easily controllable for an extended tape, and in the worst case, permits the tape to cause an injury to the user or a third person standing near the user.
2. Frequent operation of a brake device reduces the durability of a tape rule, especially in the case where the brake device includes metallic springs or screws. A high-fault rate of the brake device increases production cost of a tape rule.
3. When it is necessary to measure several objects successively, it is inconvenient because a conventional brake device is not suitable for frequent operation as described above.
4. A conventional tape rule must be securely kept out of the reach of children, as the extended tape will normally retract automatically at a very high speed, which is dangerous to a child that tampers with it.
There was an improved design for a brake device for a tape rule patented in U.S. Pat. No. 4,976,048. In this cited case, braking a tape is carried out by a toggle and its shoe. There is a pivot arm provided on the toggle, and the end of the pivot arm is formed into a U-shaped pivot recess that hooks on a bearing shaft of the shoe. An aperture is further formed on the lower end of the bearing shaft which makes the pivot arm of the toggle able to revolve around the bearing shaft of the shoe. As soon as the tape has been pulled out and positioned in a desired position thereof, the user may press an off side of the toggle to urge a brake strap against the tape by turning the pivot arm, thereby achieving the aim of halting the movement of the tape. On the other hand, when retracting the tape, by pressing an on side of the toggle, the pivot arm turns to bring the shoe off the tape so that the tape is released to wind back on the reel and it returns into the housing. With this structure, the brake device of the cited case performs the braking function of the tape. However, it should be noticed that in this structure the forces for braking and releasing the tape are concentrated in the hooked portion of the pivot arm and the bearing shaft because the shoe is driven by the pivot arm. After the tape rule has been in use for a certain time, the pivot recess formed at the end of the pivot arm is likely to crack, thereby causing the brake device to lose its function. Besides, in the event that the bearing shaft disengages from the pivot recess during braking of the tape, the tape will get stuck and fail to be wound back into the housing. In addition, a tape rule with such a brake device is too sophisticated to assemble owing to its complicated structure. That leads to an increase in the production cost and discourages users from purchasing the product.
It is an object of the present invention to provide a simply constructed, easily operable brake device for a tape rule, thereby upgrading the quality of a tape rule and minimizing its production cost.
To achieve this object, the brake device for a tape rule according to the present invention comprises a housing composed of an upper housing and a lower housing, a control device, and a brake strap. There are a pair of breaches, guide slots, positioning pins and slide slots respectively formed in the upper and the lower housings, facing each other. Main components of the brake device are the control device and the brake strap. The control device emerges out of the housing with its brake button and release button extending out of the breaches of the upper and the lower housings. The brake strap is set in the slide slots of the upper and lower housings with its one end received in a confining slit, while its other end is disposed in a position near the tape. The brake strap is further equipped with a spring tongue having a protuberance formed at its end for positioning the brake strap in the slide slots thereof. When the brake button is pressed, a supporting arm of the brake button pushes the brake strap to press against the tape and halt it thereat, while the spring tongue is blocked by the slide slot on the lower housing, and causing the spring tongue to be flexed to produce a resilient force. As soon as the releasing button is pressed, the brake strap restores its initial state with the aid of the resiliency of the spring so that the tape is released from detention and is free to retract.